Clean up some dead code and MSVC warnings.

- Dead code from experiments in SelectionBar removed.
- Many warnings about unused parameters fixed with WXUNUSED()
- Many warnings about signed / unsigned comparisons cleaned up.
- Several 'local variable declared but not used' warnings fixed.

src/prefs/KeyConfigPrefs.cpp

@@ -384,7 +384,7 @@ void KeyConfigPrefs::OnExport(wxCommandEvent & WXUNUSED(event))
 
 // There currently is only one clickable AButton
 // so we just do what it needs.
-void KeyConfigPrefs::OnDefaults(wxCommandEvent & event)
+void KeyConfigPrefs::OnDefaults(wxCommandEvent & WXUNUSED(event))
 {
    wxMenu Menu;
    Menu.Append( 1, _("Standard") );

src/prefs/MidiIOPrefs.cpp

@@ -174,11 +174,11 @@ void MidiIOPrefs::PopulateOrExchange( ShuttleGui & S ) {
 #endif
 }
 
-void MidiIOPrefs::OnHost(wxCommandEvent & e)
+void MidiIOPrefs::OnHost(wxCommandEvent & WXUNUSED(e))
 {
    wxString itemAtIndex;
    int index = mHost->GetCurrentSelection();
-   if (index >= 0 && index < mHostNames.Count())
+   if (index >= 0 && index < (int)mHostNames.Count())
       itemAtIndex = mHostNames.Item(index);
    int nDevices = Pm_CountDevices();
 

src/prefs/SpectrogramSettings.cpp

@@ -364,14 +364,14 @@ namespace
    {
       // Create the requested window function
       window = Floats{ fftLen };
-      int ii;
+      size_t ii;
 
       const bool extra = padding > 0;
       wxASSERT(windowSize % 2 == 0);
       if (extra)
          // For windows that do not go to 0 at the edges, this improves symmetry
          ++windowSize;
-      const int endOfWindow = padding + windowSize;
+      const size_t endOfWindow = padding + windowSize;
       // Left and right padding
       for (ii = 0; ii < padding; ++ii) {
          window[ii] = 0.0;
@@ -387,7 +387,7 @@ namespace
          break;
       case TWINDOW:
          NewWindowFunc(windowType, windowSize, extra, window.get() + padding);
-         for (int ii = padding, multiplier = -(int)windowSize / 2; ii < endOfWindow; ++ii, ++multiplier)
+         for (int ii = padding, multiplier = -(int)windowSize / 2; ii < (int)endOfWindow; ++ii, ++multiplier)
             window[ii] *= multiplier;
          break;
       case DWINDOW: